Variable valve timing apparatus

ABSTRACT

A phase adjusting mechanism is engaged with a brake shaft, and adjusts a rotation phase between a crankshaft and a camshaft according to a braking torque acting on a rotor. The rotation phase is adjusted in a predetermined direction when the braking torque is increased. A torque input mechanism inputs a return torque into the phase adjusting mechanism to return the rotation phase in an opposite direction opposite from the predetermined direction. The torque input mechanism increases the return torque corresponding to the rotation phase as an environmental temperature of the variable valve timing apparatus is lowered.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2011-130492filed on Jun. 10, 2011, the disclosure of which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a variable valve timing apparatus.

BACKGROUND

A fluid brake device conducts variable control of viscosity of magneticviscosity fluid by causing a magnetic flux to pass through the magneticviscosity fluid. The magnetic viscosity fluid is filled in a fluidchamber of a casing, and contacts a brake rotor. Braking torque isprovided to the brake rotor of the fluid brake device with comparativelysmall electric power, so that the fluid brake device is suitably used ina variable valve timing apparatus that controls a relative engine phasebetween a crankshaft and a camshaft of an engine in accordance with thebraking torque.

JP-A-2008-51093 describes a variable valve timing apparatus having acasing, a brake shaft penetrating the casing, and a phase adjustingmechanism engaged with the brake shaft. If the braking torque acting onthe brake rotor is increased, the phase adjusting mechanism adjusts theengine phase in a direction advancing the valve timing.

The variable valve timing apparatus further includes an elastic memberthat inputs a return torque to the phase adjusting mechanism to returnthe engine phase in a direction retarding the valve timing. Theintensity of the return torque corresponds to the engine torque. If thebraking torque input into the brake rotor is decreased, the engine phaseis returned to the retarding direction by the return torque input fromthe elastic member. Thus, the engine phase can be controlled inaccordance with the braking torque acting on the brake rotor bycontrolling the viscosity of the magnetic viscosity fluid.

However, as a temperature of the magnetic viscosity fluid is lowered,the viscosity of the magnetic viscosity fluid becomes high. When theenvironmental temperature of the variable valve timing apparatus isrelatively low, for example, immediately after the engine is started,the low-temperature magnetic viscosity fluid has high viscosity, so thatthe braking torque is increased. Even if the magnetic flux passingthrough the magnetic viscosity fluid is weakened, it is difficult toretard the valve timing. Thus, at the low-temperature time, it may bedifficult to control the engine phase by variably controlling theviscosity of the magnetic viscosity fluid.

If the return torque is increased for the low-temperature time, thereturn torque remains high when the environmental temperature is raisedby the continuous operation of the engine. On the other hand, thebraking torque input into the brake rotor is decreased by the loweringin the viscosity of the magnetic viscosity fluid when the environmentaltemperature is raised. In this case, it is difficult to balance thereturn torque and the braking torque, so that the engine phase maybecome unstable in the ordinary temperature time.

SUMMARY

According to an example of the present disclosure, a variable valvetiming apparatus that controls valve timing of a valve which is openedand closed by a camshaft driven by torque transmission from a crankshaftin an internal combustion engine includes a case, magnetic viscosityfluid, a control device, a rotor, a phase adjusting mechanism, and atorque input mechanism. The case defines a fluid chamber inside. Themagnetic viscosity fluid is kept in the fluid chamber, and has aviscosity variable in accordance with magnetic flux passing through. Thecontrol device carries out variable control of the viscosity of themagnetic viscosity fluid by varying the magnetic flux. The rotor has abrake shaft penetrating the case to come into contact with the magneticviscosity fluid so that the rotor receives a braking torque according tothe viscosity of the magnetic viscosity fluid. The phase adjustingmechanism is engaged with the brake shaft at an outside of the case, andadjusts a rotation phase between the crankshaft and the camshaftaccording to the braking torque acting on the rotor. The rotation phaseis adjusted in a predetermined direction when the braking torque isincreased. The torque input mechanism inputs a return torque into thephase adjusting mechanism to return the rotation phase in an oppositedirection opposite from the predetermined direction. The torque inputmechanism increases the return torque corresponding to the rotationphase as an environmental temperature of the variable valve timingapparatus is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present disclosure will be morereadily apparent from the following detailed description when takentogether with the accompanying drawings. In which:

FIG. 1 is a schematic sectional view illustrating a variable valvetiming apparatus including a fluid brake device according to a firstembodiment of the present disclosure;

FIG. 2 is a sectional view taken along a line II-II of FIG. 1;

FIG. 3 is a sectional view taken along a line of FIG. 1;

FIG. 4 is a graph illustrating characteristics of magnetic viscosityfluid of the fluid brake device;

FIG. 5 is a sectional view taken along a line V-V of FIG. 1;

FIG. 6A is a sectional view illustrating a return torque input mechanismof the fluid brake device at a low-temperature time, and FIG. 6B is asectional view illustrating the return torque input mechanism at anordinary temperature time;

FIG. 7A is a sectional view illustrating a return torque input mechanismof a fluid brake device according to a second embodiment at alow-temperature time, and FIG. 7B is a sectional view illustrating thereturn torque input mechanism of the second embodiment at an ordinarytemperature time; and

FIG. 8A is a sectional view illustrating a return torque input mechanismof a fluid brake device according to a third embodiment at alow-temperature time, and

FIG. 8B is a sectional view illustrating the return torque inputmechanism of the third embodiment at an ordinary temperature time.

DETAILED DESCRIPTION

A plurality of embodiments of the present disclosure are explainedreferring to drawings. Components and parts corresponding to thecomponents and parts described in the preceding description may beindicated by the same reference number and may not be describedredundantly. In a case that only a part of component or part isdescribed, other descriptions for the remaining part of component orpart in the other description may be incorporated. The embodiments canbe partially combined or partially exchanged in some forms which areclearly specified in the following description. In addition, it shouldbe understood that, unless trouble arises, the embodiments can bepartially combined or partially exchanged each other in some forms whichare not clearly specified.

First Embodiment

FIG. 1 is a cross-sectional view taken along a line I-I of FIG. 2 andshows a variable valve timing apparatus 1 having a fluid brake device100 according to a first embodiment. The variable valve timing apparatus1 is mounted on an engine of a vehicle. The variable valve timingapparatus 1 is installed in a torque transmission train which transmitsengine torque to a camshaft 2 from a crankshaft (not shown). Thecamshaft 2 opens and closes an intake valve (not shown) of the enginethrough the transmission of the engine torque. The variable valve timingapparatus 1 controls a valve timing of the intake valve.

The variable valve timing apparatus 1 has a control circuit 200 and aphase adjusting mechanism 300 in addition to the fluid brake device 100.The control circuit 200 is a circuit supplying energizing current. Thevariable valve timing apparatus 1 provides appropriate valve timing forthe engine by adjusting an engine phase which is a relative angularphase between the camshaft 2 and the crankshaft.

The fluid brake device 100 is provided with a case 110, a brake rotor130, a magnetic viscosity fluid 140, a sealing device 160 and a solenoidcoil 150.

The case 110 is formed in a hollow shape as a whole. The case 110 has afixing member 111 and a cover member 112. The fixing member 111 has acylindrical shape in which outside diameter is changed to form a step,and is made of magnetic materials. The fixing member 111 is fixed to amember of the engine, such as a chain cover (not shown). The covermember 112 has a round disc shape, and is made of magnetic materials.The cover member 112 is arranged to have the same axis as the fixingmember 111, and opposes the phase adjusting mechanism 300 through thefixing member 111. The fixing member 111 and the cover member 112 areliquid-tightly tightened to form the case 110 and to define a fluidchamber 114 therebetween.

The rotor 130 includes a shaft 131 and a plate 132 securely fixed eachother. The shaft 131 extends in an axis direction, and is made ofmagnetic materials. The shaft 131 penetrates the fixing member 111 ofthe case 110 between an inside and an outside of the case 110. One endof the shaft 131 extends to the outside of the case 110, and is engagedwith the phase adjusting mechanism 300 at the outside of the case 110.Intermediate part of the shaft 131 is rotatably supported by a bearing116 defined in the fixing member 111. Since the phase adjustingmechanism 300 receives the engine torque from the crankshaft, the rotor130 receives a rotating torque in a counterclockwise direction in FIGS.2 and 3 from the phase adjusting mechanism 300.

As shown in FIG. 1, the annular plate 132 made of magnetic materials isdisposed on an outer surface of the shaft 131 and is located on an endportion of the shaft 131 opposite from the phase adjusting mechanism300. The plate 132 spreads outward in the radial direction, and isaccommodated in the fluid chamber 114. In the fluid chamber 114, theplate 132 and the fixing member 111 define a magnetic gap 114 a in theaxis direction. Similarly, the plate 132 and the cover member 112 definea magnetic gap 114 b in the axis direction.

The magnetic viscosity fluid 140 is filled in the fluid chamber 114having the magnetic gaps 114 a and 114 b. The magnetic viscosity fluid140 is a kind of functional fluid. For example, the magnetic viscosityfluid 140 contains magnetic particles which are suspended innon-magnetic base liquid. For example, oil which is the same kind oflubrication oil for the internal combustion engine may be used as thebase liquid. A powdered magnetic material such as carbonyl iron etc. maybe used as the magnetic particles for the magnetic viscosity fluid 140.

Viscosity of the magnetic viscosity fluid 140 is varied according to amagnetic field intensity applied. In other word, viscosity of themagnetic viscosity fluid 140 is varied according to a magnetic fluxdensity. As shown in FIG. 4, viscosity of the magnetic viscosity fluid140 is raised according to increase in the magnetic flux density.Therefore, the yield stress is increased in proportion to the viscosity.

As shown in FIG. 1, the sealing device 160 is arranged between the fluidchamber 114 and the bearing 116 in the axis direction of the case 110.The sealing device 160 seals a space between the fixing member 111 ofthe case 110 and the shaft 131 of the brake rotor 130, therebyrestricting the magnetic viscosity fluid 140 from leaking outside of thecase 110.

Specifically, the shaft 131 of the brake rotor 130 has a guide rotor 134continuously extending in the rotation direction. A magnetism sealingsleeve 170 is arranged to surround the outer circumference side of theshaft 131 in the rotation direction. The sealing sleeve 170 has apermanent magnet 171 and a pair of guide yokes 174, 175. A seal gap 180is defined between the guide yoke 174 and the guide rotor 134 and a sealgap 181 is defined between the guide yoke 175 and the guide rotor 134.The seal gap 180, 181 communicates with the fluid chamber 114.

A magnetic flux generated by the permanent magnet 171 is guided from theguide yoke 174, 175 through the seal gap 180, 181 to the guide rotor134. The magnetic flux having high density passes through the seal gap180, 181, and the viscosity of the magnetic viscosity fluid 140 israised by the high density magnetic flux. Thereby, the magneticviscosity fluid 140 is caught in a film shape at the seal gap 180, 181,and works as a self-sealing film that restricts the magnetic viscosityfluid 140 from leaking.

The solenoid coil 150 is produced by winding a metal wire on a radialoutside surface of a cylindrical bobbin 151. The solenoid coil 150 isdisposed on a radial outside part of the plate 132 in a coaxial manner.The solenoid coil 150 is supported in the case 110, and is interposedbetween the fixing member 111 and the cover member 112 in the axisdirection. The solenoid coil 150 is excited by being supplied withelectric current, and generates a magnetic flux which passes through thefixing member 111, the magnetic gap 114 a, the plate 132, the magneticgap 114 b, and the cover member 112.

When the solenoid coil 150 generates the magnetic flux duringcounterclockwise rotation of the rotor 130 shown in FIGS. 2 and 3, themagnetic flux passes through the magnetic viscosity fluid 140 of themagnetic gaps 114 a and 114 b of the fluid chamber 114. The viscosity ofthe magnetic viscosity fluid 140 is varied by the magnetic flux, and abraking torque is generated between the case 110 and the rotor 130 whichcome in contact with the magnetic viscosity fluid 140. Therefore, theplate 132 of the rotor 130 receives the braking torque in the clockwisedirection in FIGS. 2 and 3, due to the viscosity resistance. As aresult, the braking torque according to the viscosity of the magneticviscosity fluid 140 is applied to the rotor 130 by supplying themagnetic flux from the solenoid coil 150.

The control circuit 200 controls current supplied to the solenoid coil150. The control circuit 200 is mainly constructed by a microcomputer.The control circuit 200 is disposed separately from the fluid brakedevice 100. The control circuit 200 is electrically connected with thesolenoid coil 150 and a battery 4 arranged in the vehicle. During a stopof the engine, the control circuit 200 turns off a current supply to thesolenoid coil 150 in response to a turning off an electric power supplyfrom the battery 4. At this time, the solenoid coil 150 does notgenerate the magnetic flux, and does not generate the braking torque onthe rotor 130.

On the other hand, during an operation of the engine, the controlcircuit 200 is supplied with the electric power from the battery 4, andcontrols an amount of current supply to the solenoid coil 150. As aresult, the solenoid coil 150 generates a regulated amount of themagnetic flux which passes through the magnetic viscosity fluid 140. Atthis time, variable control of the viscosity of the magnetic viscosityfluid 140 is carried out. The braking torque applied to the rotor 130 isadjusted by the amount of the current supplied to the solenoid coil 150.

As shown in FIG. 1, the phase adjusting mechanism 300 includes a drivingrotor 10, a driven rotor 20, a returning member 30, a planetary carrier40, and a planetary gear 50.

The driving rotor 10 includes a gear member 12 and a chain wheel 13which are made of metal. The gear member 12 and the chain wheel 13 areformed in cylindrical shapes and are fastened by screws in a coaxialmanner. As shown in FIG. 2, the gear member 12 has a radial insidesurface where a driving inner gear 14 is formed. A teeth tip circle hasa diameter smaller than that of a teeth bottom circle in the gear 14. Asshown in FIG. 1, the chain wheel 13 has a radial outside surface where aplurality of gear teeth 16 is formed. The gear teeth 16 of the chainwheel 13 is engaged with the crankshaft via a timing chain (not shown)and rotated synchronously with the crankshaft. Therefore, the drivingrotor 10 is rotated in the counterclockwise direction in FIGS. 2 and 3in response to the rotation of the crankshaft when the engine torque istransmitted to the chain wheel 13 from the crankshaft through the timingchain.

As shown in FIG. 1, the driven rotor 20 is formed in a cylindrical shapeand is arranged in a radial inside of the chain wheel 13 in a coaxialmanner. The driven rotor 20 has a connection part 21 on the bottom walland the connection part 21 is fitted and connected to the camshaft 2 ina coaxial manner using screw. The driven rotor 20 is able to rotate inresponse to the rotation of the camshaft 2 and is able to have relativerotation relative to the driving rotor 10. The rotation direction of thedriven rotor 20 is set in the counterclockwise direction of FIGS. 2 and3, similarly to the driving rotor 10. The driven rotor 20 is interlockedwith the camshaft 2, and is supported to relatively rotate with respectto the driving rotor 10.

As shown in FIG. 3, the driven rotor 20 has a radial inside surfacewhere a driven inner gear 22 is formed. A teeth tip circle has adiameter smaller than that of a teeth bottom circle in the gear 22. Theinside diameter of the driven inner gear 22 is set larger than that ofthe driving inner gear 14, and the number of teeth of the driven innergear 22 is set greater than the number of teeth of the driving innergear 14. The driven inner gear 22 is positioned away from the drivinginner gear 14 in the axis direction, in a direction opposite from thefluid brake device 100.

As shown in FIG. 1, the returning member 30 consists of a helicaltorsion metal spring. The returning member 30 is coaxially arranged inan inside of the chain wheel 13. The returning member 30 has one end 31which is engaged with the chain wheel 13 and the other end 32 which isengaged with the connection part 21. The returning member 30 generatesassist torque when the returning member 30 is twisted between the rotors10 and 20. The assist torque urges and pushes the driven rotor 20 in aretarding direction with respect to the driving rotor 10.

As shown in FIGS. 1-3, the planetary carrier 40 is formed in acylindrical shape as a whole and is made of metal. The planetary carrier40 has a radial inside surface where a transfer part 41 which receivesthe braking torque from the rotor 130 is formed. The transfer part 41 iscoaxially arranged with the rotors 10 and 20. The transfer part 41 has apair of engaging grooves 42 and a connector 43 fitted with the grooves42. The transfer part 41 of the planetary carrier 40 and the brake shaft131 are engaged via the connector 43. The planetary carrier 40 iscapable of rotating with the brake rotor 130, and is capable of havingrelative rotation relative to the driving rotor 10. The rotationdirection of the planetary carrier 40 is set in the counterclockwisedirection in FIGS. 2 and 3 when the engine is active, similarly to thebrake rotor 130.

As shown in FIGS. 1-3, the planetary carrier 40 has a supporting portion46 which supports the planetary gear 50. The supporting portion 46 islocated eccentrically with respect to the rotors 10 and 20 and the brakeshaft 131, and is coaxially engaged with a center hole 51 of theplanetary gear 50 through a planetary bearing 48. The planetary gear 50is supported by the supporting portion 46 in such a manner as to performthe planetary motion. The planetary gear 50 rotates about an eccentricaxis of the supporting portion 46, and also the planetary gear 50revolves relative to the planetary carrier 40. Thus, when the planetarycarrier 40 performs relative rotation with respect to the driving rotor10 in the revolution direction of the planetary gear 50, the planetarygear 50 performs the planetary motion.

The planetary gear 50 has a radial outside surface formed in a steppedcylindrical shape. The planetary gear 50 has a driving outer gear 52 anda driven outer gear 54 on the radial outside. The driving outer gear 52is formed on a smaller diameter part of the gear 50, and the drivenouter gear 54 is formed on a larger diameter part of the gear 50. Thedriving outer gear 52 and the driven outer gear 54 are coaxiallyarranged. The driving outer gear 52 intermeshes with the driving innergear 14 only at a position where the planetary gear 50 is located by itsorbiting motion. The driven outer gear 54 also intermeshes with thedriven inner gear 22 only at a position where the planetary gear 50 islocated by its orbiting motion. The outside diameter of the driven outergear 54 is set larger than that of the driving outer gear 52, and thenumber of teeth of the outer gear 52, 54 is set smaller than the numberof teeth of the inner gear 22, 14 by the same number.

The phase adjusting mechanism 300 adjusts the engine phase according toa balance of torques among the braking torque input into the rotor 130,the assist torque of the returning member 30 acting in the oppositedirection of the braking torque, and fluctuating torque acting on thecamshaft 2 during the operation of the engine.

In a case where the braking torque is adjusted in a constant value inorder to enable the rotor 130 to rotate with the drive rotor 10 in thesame rotating speed, the planetary carrier 40 does not rotate relativelywith respect to the driving inner gear 14. Then, the planetary gear 50orbits synchronously with both the rotors 10 and 20 without performingrelative rotation of the sun-and-planet motion. Therefore, the enginephase is maintained in a constant angular phase.

In a case where the braking torque is increased in order to enable therotor 130 to rotate at a rotating speed that is slower than that of thedrive rotor 10, the planetary carrier 40 relatively rotates in aretarding direction with respect to the driving inner gear 14. Then, theplanetary gear 50 itself rotates by the sun-and-planet motion and orbitson the gears 14 and 22. Therefore, the driven rotor 20 is relativelyrotated in an advancing direction with respect to the drive rotor 10.Therefore, the engine phase is advanced.

In a case where the braking torque is decreased in order to enable therotor 130 to rotate at a rotating speed that is higher than that of thedrive rotor 10, the planetary carrier 40 relatively rotates in anadvancing direction with respect to the driving inner gear 14. Then, theplanetary gear 50 itself rotates by the sun-and-planet motion and orbitson the gears 14 and 22. Therefore, the driven rotor 20 is relativelyrotated in a retarding direction with respect to the drive rotor 10.Therefore, the engine phase is retarded.

As shown in FIG. 5, a return torque input mechanism 60 is constructed bya thermo sensor element 70 and a holding member 80, in addition to thereturning member 30.

As shown in FIG. 1, the returning member 30 is constructed by a wirespirally winded, as a main part 30 a. The one end 31 of the returningmember 30 is received by the thermo sensor element 70 through apillar-shaped connection component 31 a made of metal materials. The oneend 31 of the returning member 30 is extended to the outer circumferenceside from the main part 30 a of the returning member 30. The other end32 of the returning member 30 is received by a stationary portion 21through a boss 32 a embedded in the stationary portion 21.

The returning member 30 is connected with the phase adjusting mechanism300. As the engine phase is adjusted in the advancing directionadvancing the valve timing, the returning member 30 is twisted at thecenter axis, so that strong recovery force is acted to the phaseadjusting mechanism 300 from the returning member 30. That is, thereturning member 30 inputs a return torque corresponding to the enginephase into the phase adjusting mechanism 300, and the return torquecauses the engine phase to return in the retarding direction retardingthe valve timing.

The thermo sensor element 70 is arranged at periphery side of thereturning member 30, and is connected with the returning member 30. Thethermo sensor element 70 has a case part 71, a wax 74, a piston 76, anda diaphragm 75, as shown in FIG. 5.

The case part 71 has a cylindrical shape, and is made of metallicmaterial which is excellent in heat conduction, for example. A waxchamber 72 is defined inside of the case part 71. The wax 74 isaccommodated in the wax chamber 72. An environmental temperature of thevariable valve timing apparatus 1 is transmitted to the wax chamber 72through the holding member 80 and the case part 71.

The wax 74 is paraffin wax, for example, and is enclosed within the waxchamber 72 of the case part 71. The volume of the wax 74 is decreased,as the temperature of the wax 74 is lowered. The volume of the wax 74 isincreased, as the temperature of the wax 74 is raised. The volume of thewax chamber 72 of the case part 71 is varied by theexpansion/contraction of the wax 74.

The piston 76 penetrates the case part 71 between the inside and theoutside of the case part 71, and is movable relative to the case part71. The piston 76 has a holding part 78 and a pressure receiving part77. The holding part 78 is constructed by a portion of the piston 76located outside of the case part 71, and holds the connection component31 a. Thereby, the piston 76 is connected with the one end 31 of thereturning member 30 through the connection component 31 a.

The pressure receiving part 77 has a board shape and defines the waxchamber 72 inside of the case part 71. The pressure receiving part 77displaces the piston 76 in the axis direction of the case part 71 by thepressure received from the wax 74 when the wax 74 has theexpansion/contraction. The piston 76 moves relative to the case part 71by being displaced by the expansion/contraction of the wax 74, so thatthe piston 76 increases the amount of elastic deformation of thereturning member 30 outside of the case part 71.

The diaphragm 75 has a ring shape and is made of rubber material whichcan be expanded or contracted. The diaphragm 75 is arranged between theouter circumference wall of the pressure receiving part 77 of the piston76 and the inner circumference wall of the case part 71, and is joinedwith the outer circumference wall and the inner circumference wall. Thediaphragm 75 expands and contracts in response to the displacement ofthe piston 76, so as to maintain the definition of the wax chamber 72inside of the case part 71. That is, the diaphragm 75 works as a sealingdevice, so that the wax 74 is restricted from leaking out of the waxchamber 72.

The holding member 80 has a disc shape and is made of metallic material.The holding member 80 is fixed to the chain wheel 13 by plural fasteningcomponents 82. A thermo sensor chamber 81 is defined in the holdingmember 80, and has a shape corresponding to the thermo sensor element70. The holding member 80 holds the thermo sensor element 70 in thethermo sensor chamber 81 in the state where the piston 76 can have thedisplacement.

If the variable valve timing apparatus 1 is left under low-temperatureenvironment in a state where the engine is stopped, the environmentaltemperature of the variable valve timing apparatus 1 is also loweredwith progress of time. The temperature of the magnetic viscosity fluid140 accommodated in the variable valve timing apparatus 1 is alsolowered to the same degree as the environmental temperature. Thereby,the viscosity of the oil, which is the base liquid of the magneticviscosity fluid 140, is raised as shown in a broken line of FIG. 4.

Therefore, the braking torque which acts on the brake rotor 130 from themagnetic viscosity fluid 140 will increase. In addition, in the insideof the phase adjusting mechanism 300, the viscosity of the lubricationoil is also raised by the lowering in the temperature of the lubricationoil. Therefore, as the environmental temperature of the variable valvetiming apparatus 1 is lowered, the torque required to adjust the enginephase in the phase adjusting mechanism 300 is increased.

The return torque input mechanism 60 increases the return torque inputinto the phase adjusting mechanism 300, as the environmental temperatureof the variable valve timing apparatus 1 is lowered. Details ofoperation of the return torque input mechanism 60 will be explained withreference to FIGS. 6A and 6B.

In low-temperature environment (e.g., about −30° C.) immediately afterstart-up of the engine, as the environmental temperature of the variablevalve timing apparatus 1 is lowered, the temperature of the thermosensor element 70 is also lowered. Therefore, as shown in FIG. 6A, thewax 74 accommodated in the wax chamber 72 of the thermo sensor element70 is contracted. At this time, the piston 76 moves to follow thecontracted wax 74, so that the piston 76 is displaced in thecounterclockwise direction shown in FIG. 6A. The displacement of thepiston 76 is transmitted to the returning member 30 through theconnection component 31 a, therefore the thermo sensor element 70further increases the amount of elastic deformation of the returningmember 30.

Thus, the recovery force of the returning member 30 which acts on thephase adjusting mechanism 300 becomes still stronger, because a set loadof the returning member 30 is increased. Therefore, the return torqueinput into the phase adjusting mechanism 300 is increased by thelowering in the environmental temperature in all the range of the enginephase adjusted with the phase adjusting mechanism 300. Accordingly, thereturn torque input mechanism 60 increases the return torque input intothe phase adjusting mechanism 300, as the environmental temperature ofthe variable valve timing apparatus 1 is lowered. In addition, the setload of the returning member 30 mentioned above represents a powerelastically deforming the returning member 30 in a case where the enginephase has the most retarded phase in the phase adjusting mechanism 300.

When the environmental temperature of the variable valve timingapparatus 1 is raised to an ordinary temperature (e.g., about 130° C.)by continuous operation of the engine, the temperature of the thermosensor element 70 is also raised. Therefore, the wax 74 accommodated inthe wax chamber 72 of the thermo sensor element 70 is expanded, as shownin FIG. 6B. The piston 76 is displaced in the clockwise rotation shownin FIG. 6B by the pressure of the expanding wax 74. The displacement ofthe piston 76 is transmitted to the returning member 30 through theconnection component 31 a, therefore the thermo sensor element 70decreases the amount of elastic deformation of the returning member 30.

Then, because the set load of the returning member 30 decreases, therecovery force of the returning member 30 which acts on the phaseadjusting mechanism 300 becomes weak. Thus, the return torque input intothe phase adjusting mechanism 300 is decreased by the raising in theenvironmental temperature in all the range of the engine phase adjustedwith the phase adjusting mechanism 300. Accordingly, the return torqueinput mechanism 60 decreases the return torque input into the phaseadjusting mechanism 300, as the environmental temperature of thevariable valve timing apparatus 1 is raised.

In the first embodiment, the braking torque input into the brake rotor130 and the torque required for adjusting the engine phase are assumedto increase due to the lowering in the environmental temperature. Atthis time, the return torque input mechanism 60 can cause the valvetiming to return in the retarding direction by increasing the returntorque, while the engine phase is advanced by the increase in thebraking torque. That is, even in the low-temperature time, the enginephase can be adjusted by the phase adjusting mechanism 300 through thevariable control of the viscosity of the magnetic viscosity fluid 140.

When the environmental temperature of the variable valve timingapparatus 1 becomes to have the ordinary temperature, the braking torqueinput into the brake rotor 130 from the magnetic viscosity fluid 140 isdecreased due to the lowering in the viscosity of the magnetic viscosityfluid 140 in response to the rise in the temperature. At this time, thereturn torque input mechanism 60 makes it easy to balance the returntorque and the braking torque input into the brake rotor 130 bydecreasing the return torque input into the phase adjusting mechanism300. Thus, in the ordinary temperature time, the engine phase can bemaintained as stable by the phase adjusting mechanism 300 through thevariable control of the viscosity of the magnetic viscosity fluid 140.

According to the first embodiment, the engine phase can be suitableadjusted at the low-temperature time, and the engine phase can bemaintained as stable at the ordinary temperature time, due to thevariable valve timing apparatus 1.

In addition, according to the first embodiment, the construction of thereturn torque input mechanism 60 can be simplified using the wax 74 thatis contracted as the environmental temperature is lowered and the piston76 that is displaced by the contraction of the wax 74. Further, thereliability of the return torque input mechanism 60 is raised by thesimplification of the return torque input mechanism 60. Therefore, thereturn torque input mechanism 60 can increase the return torque as theenvironmental temperature of the variable valve timing apparatus 1 islowered, with more reliability. Thus, the engine phase can be suitableadjusted at the low-temperature time, and the engine phase can bemaintained as stable at the ordinary temperature time, with morereliability.

In the first embodiment, the returning member 30 may correspond to anelastic member. The return torque input mechanism 60 may correspond to atorque input mechanism. The thermo sensor element 70 may correspond to adeformation increasing portion that increases the deformation amount ofthe elastic member. The wax chamber 72 may correspond to anaccommodation chamber. The casing part 71 may correspond to acontraction casing. The wax 74 may correspond to a contraction part. Thepiston 76 may correspond to a displacement part. The control circuit 200and the solenoid coil 150 may correspond to a control device thatcontrols the viscosity of the magnetic viscosity fluid. The advancingdirection of the valve timing may correspond to a predetermineddirection. The retarding direction of the valve timing may correspond toan opposite direction opposite from the predetermined direction.

Second Embodiment

A second embodiment, which is a modification of the first embodiment,will be described with reference to FIGS. 7A and 7B. The thermo sensorelement 70 of the second embodiment further includes a coil spring 279.The coil spring 279 is formed by a wire spirally winded around thepiston 76, and is made of metallic materials. The coil spring 279 isaccommodated in a space opposite from the wax chamber 72 through thepressure receiving part 77 in the state where the coil spring 279 iscontracted in the axis direction, in the case part 71. Hereinafter, thespace is referred as a spring chamber 273. In the inside of the casepart 71, the coil spring 279 biases the pressure receiving part 77 ofthe piston 76 toward the wax 74.

Operation of the return torque input mechanism 60 with the coil spring279 will be explained below.

As the environmental temperature of the variable valve timing apparatus1 is lowered, the wax 74 contracts, and the piston 76 moves to followthe contracted wax 74 so that the piston 76 is displaced in thecounterclockwise direction shown in FIG. 7A. Because the coil spring 279biases the piston 76 toward the wax 74, the piston 76 suitably followsthe contracted wax 74 and is displaced with reliability. Thedisplacement of the piston 76 further increases the amount of elasticdeformation of the returning member 30, so that the recovery force ofthe returning member 30 which acts on the phase adjusting mechanism 300becomes still stronger. Thus, the return torque input mechanism 60 canincrease the return torque input into the phase adjusting mechanism 300certainly, as the environmental temperature of the variable valve timingapparatus 1 is lowered.

Moreover, as shown in FIG. 7B, as the temperature of the variable valvetiming apparatus 1 is raised to the ordinary temperature, the wax 74expands. Thereby, the pressure of the expanding wax 74 displaces thepiston 76 in the clockwise rotation by resisting the biasing force ofthe coil spring 279. The displacement of the piston 76 decreases theamount of elastic deformation of the returning member 30, so that therecovery force of the returning member 30 which acts on the phaseadjusting mechanism 300 becomes weak. Thus, as the environmentaltemperature of the variable valve timing apparatus 1 is raised, thereturn torque input mechanism 60 can decrease the return torque inputinto the phase adjusting mechanism 300.

According to the second embodiment, the thermo sensor element 70 has thecoil spring 279. Therefore, as the environmental temperature of thevariable valve timing apparatus 1 is lowered, the return torque inputmechanism 60 increases the return torque with reliability. Thus, theengine phase can be suitably adjusted at the low-temperature time, andthe engine phase can be maintained as stable at the ordinary temperaturetime, due to the variable valve timing apparatus 1.

The coil spring 279 of the second embodiment may correspond to a biasingpart.

Third Embodiment

A third embodiment, which is a modification of the second embodiment,will be described with reference to FIGS. 8A and 8B. A thermo sensorelement 370 of the third embodiment is arranged at the clockwisedirection side of the connection component 31 a. In the thermo sensorelement 370, arrangement of the wax chamber 72 and the spring chamber273 is reverse in the axis direction of the case part 71, compared withthe thermo sensor element 70 of the first and second embodiments. Thewax chamber 72 defined in the case part 71 is located between theholding part 78 and the pressure receiving part 77. Moreover, the springchamber 273 defined in the case part 71 is located on the clockwisedirection side of the pressure receiving part 77, that is separated fromthe holding part 78. Operation of the return torque input mechanism 60with the thermo sensor 370 of the third embodiment will be explainedbelow.

When the environmental temperature of the variable valve timingapparatus 1 is lowered, the wax 74 is contracts, and the piston 76 movesto follow the contacted wax 74 so that the piston 76 is displaced in thecounterclockwise rotation shown in FIG. 8A, due to the biasing force ofthe coil spring 279. The displacement of the piston 76 further increasesthe amount of elastic deformation of the returning member 30, so thatthe recovering force of the returning member 30 which acts on the phaseadjusting mechanism 300 becomes still stronger. Thus, the return torqueinput mechanism 60 can increase the return torque input into the phaseadjusting mechanism 300 certainly, as the environmental temperature ofthe variable valve timing apparatus 1 is lowered.

Moreover, as shown in FIG. 8B, as the temperature of the variable valvetiming apparatus 1 is raised to the ordinary temperature, the wax 74expands. Thereby, the pressure of the expanding wax 74 displaces thepiston 76 in the clockwise rotation by resisting the biasing force ofthe coil spring 279. The displacement of the piston 76 decreases theamount of elastic deformation of the returning member 30, so that therecovery force of the returning member 30 which acts on the phaseadjusting mechanism 300 becomes weak. Thus, as the environmentaltemperature of the variable valve timing apparatus 1 is raised, thereturn torque input mechanism 60 can decrease the return torque inputinto the phase adjusting mechanism 300.

According to the thermo sensor 370 of the third embodiment, the returntorque input mechanism 60 can increase or decrease the return torqueinput into the phase adjusting mechanism 300 so as to respond to theenvironmental temperature. Therefore, the variable valve timingapparatus 1 of the third embodiment can suitably adjust the engine phaseat the low-temperature time, and can maintain the engine phase as stableat the ordinary temperature time.

Other Embodiments

The present disclosure should not be limited to the above embodiments,but may be implemented in other ways without departing from the spiritof the disclosure.

The deformation increasing portion is not limited to the thermo sensorelement 70. Alternatively, the deformation increasing portion may beconstructed by a temperature detector that detects the environmentaltemperature of the variable valve timing apparatus 1, and an actuatorthat is displaced to increase the amount of elastic deformation of thereturning member 30 as the temperature detected by the detector islowered. Furthermore, the elastic member such as the returning member 30may be omitted. In this case, the variable valve timing apparatus 1 maybe equipped with an actuator that increases the return torque as thetemperature detected by the detector is lowered, as a torque inputmechanism.

Although the present disclosure is applied to the intake valve, thepresent disclosure may be applied to an apparatus for controlling valvetiming of an exhaust valve. In this case, the retarding direction maycorrespond to a predetermined direction, and the advancing direction maycorrespond to an opposite direction opposite from the predetermineddirection.

The elastic member is not limited to the returning member 30.Alternatively, the elastic member may be a coil spring, plate spring,etc., or may be made of rubber material.

The contraction part is not limited to the wax 74 in semi-solid state.The contraction part may be other component that is contracted as theenvironmental temperature of the variable valve timing apparatus 1 islowered. Further, the contraction part may be in a solid state, a liquidstate, or a gas state.

More specifically, the contraction part may be a spring made of a shapememory alloy, and the shape of the spring is changed by the temperature.The shape memory alloy may be an alloy of titanium and nickel, forexample. The spring made of the shape memory alloy is contracted as theenvironmental temperature of the variable valve timing apparatus 1 islowered, and will be recovered into the initial shape as theenvironmental temperature of the variable valve timing apparatus 1 israised. In this case, the thermo sensor element corresponding to thedeformation increasing portion further increases the amount of elasticdeformation of the returning member 30 under low-temperatureenvironment, so that the return torque input into the phase adjustingmechanism 300 from the returning member 30 is made stronger.

Further, the thermo sensor element corresponding to the deformationincreasing portion decreases the amount of elastic deformation of thereturning member 30 under ordinary temperature environment, so that thereturn torque input into the phase adjusting mechanism 300 from thereturning member 30 is made weak.

In addition, the shape memory alloy may be an alloy using iron as aprincipal component, and manganese and silicon are mixed into theprincipal component. Moreover, the spring may have a coil shape, a panshape or a board shape.

The engine phase may be adjusted according to the braking torque inputinto the brake rotor 130 due to the cooperation with the brake shaft131. Although the present disclosure is applied to the intake valve, thepresent disclosure may be applied to an apparatus for controlling valvetiming of an exhaust valve or an apparatus for controlling valve timingof an intake valve and an exhaust valve. Further, the present disclosuremay be applied to a variety of apparatuses using the braking torque.

Although the present disclosure has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications will become apparent to those skilled in the art. Suchchanges and modifications are to be understood as being within the scopeof the present disclosure as defined by the appended claims.

1. A variable valve timing apparatus that controls valve timing of avalve which is opened and closed by a camshaft driven by torquetransmission from a crankshaft in an internal combustion engine, theapparatus comprising: a case defining a fluid chamber inside; magneticviscosity fluid kept in the fluid chamber, the magnetic viscosity fluidhaving a viscosity variable in accordance with magnetic flux passingthrough; a control device which carries out variable control of theviscosity of the magnetic viscosity fluid by varying the magnetic flux;a rotor having a brake shaft penetrating the case to come into contactwith the magnetic viscosity fluid so that the rotor receives a brakingtorque according to the viscosity of the magnetic viscosity fluid; aphase adjusting mechanism engaged with the brake shaft at an outside ofthe case, the phase adjusting mechanism adjusting a rotation phasebetween the crankshaft and the camshaft according to the braking torqueacting on the rotor, the rotation phase being adjusted in apredetermined direction when the braking torque is increased; and atorque input mechanism inputting a return torque into the phaseadjusting mechanism to return the rotation phase in an oppositedirection opposite from the predetermined direction, wherein the torqueinput mechanism increases the return torque corresponding to therotation phase as an environmental temperature of the variable valvetiming apparatus is lowered.
 2. The variable valve timing apparatusaccording to claim 1, wherein the torque input mechanism has an elasticmember connected to the phase adjusting mechanism in a state where theelastic member has an elastic deformation, the elastic member inputtingthe return torque corresponding to the rotation phase using a recoveringforce of the elastic member from the elastic deformation, and adeformation increasing portion connected to the elastic member, thedeformation increasing portion increasing the return torque byincreasing an amount of the elastic deformation of the elastic member asthe environmental temperature of the variable valve timing apparatus islowered.
 3. The variable valve timing apparatus according to claim 2,wherein the deformation increasing portion has a contraction part thatis contacted as the environmental temperature of the variable valvetiming apparatus is lowered, a contraction casing defining anaccommodation chamber that accommodates the contraction part, and adisplacement part penetrating the contraction casing, the displacementpart increasing the amount of the elastic deformation of the elasticmember at outside of the contraction casing by being displaced by thecontraction of the contraction part in the accommodation chamber.
 4. Thevariable valve timing apparatus according to claim 3, wherein thedeformation increasing portion further has a biasing part that biasesthe displacement part toward the contraction part, inside of thecontraction casing.